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NOTE that this works on our trailblazer. From all the reading i did this should work for anyone. As all with the internet, proceed at your own devices!

If you do this or expand on it (reading values from sensors etc) please let everyone know!

To do this you need a scanner which lets you send a message by manually typing in the message. There are several of these out there, no idea which is better, worse, or the same. if you have the scantool, you need software to control it. There are free versions out there, though i opted to pay to get something which works with less hassle. The scantool.net scanner with Scan XL pro SW is on sale for $149 (not sure how often they run sales, or if this is an all the time price)

I went with the ODBLink Scan Tool from scantool.net with the scanXL Pro SW with the GM package add on since we have 3 GM vehicles.

so in summary you need a computer based scanner and software that lets you send messages manually (sometimes called terminal mode)

I figured out the messages to send to get codes from the TCCM on an 02 trailblazer, should be the same for all years.

this seems complicated, though just about anyone can do this. quite frankly you can just send the messages I listed and not delve into the details of what it all means

the messages are in Hexadecimal, don't let that scare you

I started to tool, selected ODB-II->connect and followed the instructions, then selected the "tool" tab and clicked on "ODB-II terminal", select "custom send tab", check the box "enable ODB-II terminal" in the top left. now you are ready to send messages!

Byte1 - PP - 6C - same as the first byte you sent
Byte2 - QQ - F1 - address of the scan tool (indicates the recipient)
Byte3 - RR - 1A - address of the TCCM module (indicates the originator)
Byte4 - SS - 59 - will be the byte4 you sent with 40 added to it
Byte5 - XZ - 43 - first part of code
Byte6 - ZZ - 79 - second part of code
Byte7 - YY - 93 - status (01) good, no issue (93) current code causing service light to illuminate (11) not sure, seemed to be associated to the last code raised, though I'm not sure
Byte8 - VV - 6A - check sum (ignore this, it is used to make sure the message made it without loosing data)

so bytes 4 and 5 have the code, to decipher:

$43 $79 <- from recceived message
$XZ $ZZ <- use this to decode based on the list below

the X is the first part of the code
4 = C0
8 = B0
A = B2
D = U1

ZZZ = code

for complete code put together XZZZ

so the $43 $79 is:

4 = C0
ZZZ = 379

code = C0379

if you get 00 00 for a code, then it is the end of the list - 00 00 is not a code, but an indicator teh end of the code list.

the status of this code (YY) in the example is 93 which seems to indicate the current fault. if you see 01 then that code is not currently active

send message 6C 1A F1 19 ff ff 00 - return all code status - 01 in before last means all is well. in this example the before last byte is 01 for all the entries except the last which has code 00 00 indicating the end of the list, therefor there are no codes present.

as a neat aside - I believe these to be every possible code that can be generated!

there is a special running to get the Pro SW with the $99 tool (and wireless/blue version) for a $149

I bought the wireless, though it is probably a waste of money as i use the USB cable, so the $99 would probably be a wiser choice. the wireless and bluetooth are for using a phone, though i since learned that required additional SW and is considerably limited compared to the ScanXL SW for the windows laptop.

Software - You need software which lets you send custom messages. If you are computer savy you can use hyperterminal. Since I wanted a fully featured scanner I purchased the ScanXL Pro with the GM add on. the PRO version lets you send custom message (terminal mode), the regular version does NOT - so if you go this route get ScanXL Pro

The scanner does a lot more than this. I find the SW a bit hard to use, and there are some things I don't like such as the emissions test status which I can't do in ScanXL Pro, but you can with the free tool they include ODBWiz.

Sorry to not post, but this *is* great data. I just have too many choices of scan software myself and now Android's app: Torque, to deal with yet another. But this is wonderful stuff for the archives for future searchers. Thanks!

Sorry to not post, but this *is* great data. I just have too many choices of scan software myself and now Android's app: Torque, to deal with yet another. But this is wonderful stuff for the archives for future searchers. Thanks!

I may forward this info over to the author of Torque, just to see if he can implement it.

Hello people and thanks for this valuable info. I tried this with an OBD terminal but go "No data" as reply.
2002 Trailblazer with shining "Service 4WD" light...
Does anyone have an idea where did I go wrong?

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